Plastic bottle and method of producing the same

ABSTRACT

A bottle having substantially no strain due to fluidized orientation in the bottom portion thereof which is homogeneously and uniformly drawn, and, as a result, exhibiting improved shock resistance and buckling strength in the bottom portion, featuring excellent resistance against environmental cracking at the center in the bottom portion, without developing crazing or whitening during the preservation, and offering excellent appearance. The bottle is formed by biaxially stretch-blow-molding a thermoplastic resin, and has a mouth portion, a shoulder portion, a barrel portion and a bottom portion, said bottom portion without being substantially affected by the residual strain due to orientation by fluidization.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a bottle formed by biaxiallystretch-blow-molding a thermoplastic resin and to a method of producingthe same. More particularly, the invention relates to a bottle that isparticularly oriented in the bottom portion thereof and has excellentresistance against environmental stress (ESC), shock resistance,strength and appearance in the bottom portion thereof, and to a methodof producing the same.

[0003] 2. Description of the Prior Art

[0004] Stretch-blow-molded plastic containers composed of polyesters orpolypropylenes and, particularly, polyester containers have nowadaysbeen widely used for containing liquid products such as liquiddetergents, shampoos, cosmetics, sauces such as soy sauces, etc., aswell as for containing aerated beverages such as beer, Coke, cider,etc., for the other containing beverages such as juices, mineral water,etc. and have also been used as cups for containing desserts, miso andother foods, owing to their excellent transparency and suitable degreeof gas barrier property.

[0005] The methods of producing polyester bottles can be roughly dividedinto the hot parison method and the cold parison method. According tothe former hot parison method, the preform formed by injection-moldingthe polyester is stretch-blow-molded in a hot state without beingcompletely cooled. According to the latter cold parison method, on theother hand, a polyester is injection-molded to, first, form anovercooled preform with bottom of amorphous polyester having a sizeconsiderably smaller than a final container, the preform is pre-heatedat a stretching temperature, and is stretched in the axial direction ina blowing metal mold and is stretched by blowing in the circumferentialdirection.

[0006] The preform with bottom has a mouth-and-neck portioncorresponding to the mouth-and-neck portion of a container and acylindrical portion with bottom that is stretch-blow-molded, andgenerally has the shape of a test tube as a whole when the container isa vertically elongated one. In the mouth-and-neck portion, for example,are formed an open end for being sealed and a means for engagement witha closure. In the bottom is further necessarily formed a gate portionthat protrudes outward from the center of the bottom for conducting theinjection-molding.

[0007] In the polyester bottles that have heretofore beenstretch-blow-molded, the orientation and crystallinity are mostdisturbed in the bottom portion of the bottle and, particularly, at thecentral portion thereof, causing problems such as deterioratedappearance and drop in the bottle properties.

[0008] For instance, even though the barrel portion of the PET bottle iscompletely transparent, the gate portion and the peripheries thereof ofthe preform are often whitened as generally called gate whitening. Ithas been said that this phenomenon occurs since the PET resin that isdistorted due to orientation by fluidization has a property of beingvery easily crystallized.

[0009] In order to prevent the gate whitening, the molding must beconducted under the conditions where the residual strain due tofluidization does not increase. For example, it has been known that thegate whitening takes place little as the gate diameter increases or asthe injection pressure decreases.

[0010] As the gate diameter increases, however, the diameter of theremaining portion of the gate increases, too, in the bottom portion ofthe bottle deteriorating the appearance. As the injection pressuredecreases, further, the preform is poorly molded and the injectionretention time is lengthened, resulting in a decrease in theproductivity.

SUMMARY OF THE INVENTION

[0011] The present inventors have discovered that the strain due toorientation by fluidization taking place at the time ofinjection-molding the preform still adversely affects the bottom portionof the bottle being uniformly and homogeneously stretched, adverselyaffects the resistance against cracking due to environmental stress andthe strength of the bottle even when the strain due to orientation byfluidization is on such a low level that does not cause the gatewhitening.

[0012] The object of the present invention is to provide a bottlewithout substantially strain due to orientation by fluidization in thebottom portion, the bottom portion being uniformly and homogeneouslystretched, having improved shock resistance and buckling strength,having excellent resistance against cracking due to environment at thecenter of the bottom portion, without developing crazing or whiteningduring the preservation, and exhibiting excellent appearance.

[0013] According to the present invention, there is provided a bottleformed by biaxially stretch-blow-molding and having a mouth portion, ashoulder portion, a barrel portion and a bottom portion, said bottomportion without being substantially affected by the residual strain dueto orientation by fluidization.

[0014] In the present invention, it is desired that:

[0015] (1) the bottle is formed by biaxially stretching-blow-molding apreform that is formed by compression-molding a thermoplastic resin;

[0016] (2) the preform has a difference (tmax−tmin) between a maximumthickness and a minimum thickness in the barrel portion thereof in thecircumferential direction, which is not larger than 0.07 mm;

[0017] (3) when the bottle is composed of a thermoplastic polyester, thecentral portion in the bottom portion of the bottle has a diffusescattering peak in 2θ of from 19.45 to 20.50° as measured by usingX-rays (Cu-α) falling in the direction of thickness of the containerwall, a peak position (A) at a portion on the outer surface side of thecentral portion in the bottom portion is an angle lower than that of apeak position (B) at a portion on the inner surface side of the centralportion in the bottom portion, the difference (B−A) thereof is notsmaller than 0.15 degrees, a half-value width (C) of the diffusescattering peak of X-rays in the portion on the outer surface side atthe central portion in the bottom portion is larger than a half-valuewidth (D) of the diffuse scattering peak of X-rays in the portion on theinner surface side at the central portion in the bottom portion, and thedifference (C−D) thereof is not smaller than 0.10 degrees; and

[0018] (4) the mouth portion has a support ring, and an annular grooveis formed in the inner peripheral edge in the lower surface of thesupport ring.

[0019] According to the present invention, there is further provided amethod of producing a bottle by biaxially stretch-blow-molding apre-molded article for blow molding that is obtained through the stepsof:

[0020] extruding a molten thermoplastic resin and cutting it into a massof melt of nearly a predetermined amount;

[0021] arranging a male metal mold and a female metal mold so as to moverelative to each other and supplying the mass of melt into the metalmold;

[0022] compression-molding the mass of melt into a pre-molded articlehaving a barrel portion with bottom and an annular groove formed in theinner peripheral edge in the lower surface of the support ring; and

[0023] cooling and solidifying the compression-molded article anddischarging the molded article out of the metal mold.

[0024] According to the method of the present invention, it is desiredthat:

[0025] (5) the mass of melt is compression-molded into a pre-moldedarticle while discharging the air remaining in the metal mold;

[0026] (6) fine gaps or holes are formed in a portion of the metal moldforming the bottom portion of the pre-molded article; and

[0027] (7) the male metal mold is constituted by a core metal mold and afollower metal mold surrounding the core metal mold and is allowed to beopened and closed coaxially therewith, the barrel portion with bottom ismolded by the core metal mold and the female metal mold, and the mouthportion is molded by the core metal mold and the follower metal mold.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a side view illustrating a bottle according to thepresent invention;

[0029]FIG. 2 is a diagram illustrating a sample used for the X-raydiffraction;

[0030]FIG. 3 is a diagram illustrating a method of X-ray diffraction;

[0031]FIG. 4 is a diagram illustrating how to find a peak position and ahalf-value width in the X-ray diffuse scattering;

[0032]FIG. 5 is a graph illustrating a relationship between the peakpositions and the half-value widths in the bottom portions of variousbottles;

[0033]FIG. 6 is a graph illustrating a relationship between thedifference (B−A) in the peak positions and the difference (C−D) in thehalf-value widths in the bottom portions of various bottles;

[0034]FIG. 7 is a plan view illustrating the whole arrangement of anapparatus used for a one-stage compression-molding method;

[0035]FIG. 8 is a side view of the apparatus of FIG. 7;

[0036]FIG. 9 is a plane view of an apparatus for cutting and feedingmasses of melt;

[0037]FIG. 10 is a side view illustrating the steps in the apparatus ofFIG. 9;

[0038]FIG. 11 is a side sectional view illustrating the stages in thestep of compression molding;

[0039]FIG. 12 is a side sectional view illustrating the stages in thestep of taking out the preform after the compression molding;

[0040]FIG. 13 is a sectional view illustrating a preform for blowmolding used in the present invention;

[0041]FIG. 14 is a sectional view illustrating another preform for blowmolding used in the present invention; and

[0042]FIG. 15 is a sectional view illustrating a further preform forblow molding used in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] Referring to FIG. 1 illustrating a bottle of the presentinvention, the bottle includes a mouth-and-neck portion 1, a shoulderportion 2 continuous to the mouth-and-neck portion, a barrel portion 3and a bottom portion 4 that are formed by biaxially stretch-blow-moldinga thermoplastic resin. In this embodiment, the bottom portion 4 has aself-standing structure and includes an annular grounding portion 5 inthe periphery of the bottom portion and a central dome portion 6swelling upward. A remarkable feature resides in that the center 7 inthe bottom portion of the bottle is not substantially affected by theresidual strain due to orientation by fluidization (has substantially noresidual strain due to orientation by fluidization).

[0044] In the polyester bottle obtained from a preform formed by theconventional injection molding as pointed out already, strain due toorientation by fluidization necessarily remains at the center in thebottom portion inherent from the remaining portion of the gate, and theresidual strain adversely affect properties, resistance and appearanceof the bottle.

[0045] In an extreme case, the strain due to orientation by fluidizationcan be confirmed by a phenomenon called gate whitening. In other cases,no means has been known for effectively detecting the strain.

[0046] The present inventors have succeeded in detecting the strain dueto orientation by fluidization at the center in the bottom portion ofthe bottle, and have formed a preform by subjecting the thermoplasticresin such as polyester or polypropylene to the compression molding and,particularly, to the one-stage compression molding in a manner that nostrain due to orientation by fluidization is substantially produced, andhave subjected the preform to the biaxial stretch-blow-molding in orderto produce a bottle having a bottom portion that is uniformly andhomogeneously stretched, having less strain due to orientation byfluidization in the bottom portion, and, hence, exhibiting improvedshock resistance and buckling strength in the bottom portion, excellentresistance against the environmental cracking at the center of thebottom portion, developing little crazing or whitening during thepreservation, and offering excellent appearance.

[0047] According to the study conducted by the present inventors, thestrain due to orientation by fluidization at the center in the bottomportion of the bottle can be detected as the presence of the orientedmesophase in the direction of thickness at the central portion in thebottom portion.

[0048] It has been known that the thermoplastic polyester as typicallyrepresented by a polyethylene terephthalate (PET) contains orientedmesophase in addition to amorphous phase and crystalline phase (Journalof Japanese Academy of Fibers, Vol. 40, No. 6, 1984, pp. 49-56).

[0049] That is, in the crystalline phase of PET, regularity can berecognized in the arrangement of benzene rings in the molecules. In theoriented mesophase, however, there is no regularity in the arrangementof benzene rings but a periodic structure is recognized in theorientation in the direction of fiber axes. In the case of the orientedfiber, the periodic structure is detected as a peak in the X-ray diffusescattering at 2θ=21° in the X-ray diffraction.

[0050] When the bottle of the present invention is composed of apolyester resin, the bottle exhibits such X-ray diffractioncharacteristics that the central portion in the bottom portion of thebottle has a diffuse scattering peak in 2θ of from 19.45 to 20.50° asmeasured by using X-rays (Cu-α) falling in the direction of thickness ofthe container wall, a peak position (A) at a portion on the outersurface side of the central portion in the bottom portion is an anglelower than that of a peak position (B) at a portion on the inner surfaceside of the central portion in the bottom portion, the difference (B−A)thereof is not smaller than 0.15 degrees, a half-value width (C) of thediffuse scattering peak of X-rays in the portion on the outer surfaceside at the central portion in the bottom portion is larger than ahalf-value width (D) of the diffuse scattering peak of X-rays in theportion on the inner surface side at the central portion in the bottomportion, and the difference (C−D) thereof is not smaller than 0.10degrees.

[0051] Referring to FIG. 2 illustrating a sample for measuring an X-raydiffraction image, the bottom portion of the bottle is cut into a widthof 1 mm in the direction of thickness inclusive of the center 7 of thebottom portion, and the surface is polished to obtain a sample 70. Aportion 72 on the inner surface side is set at a position separated awayby 100 μm from the inner surface 71 of the sample, a portion 74 on theouter surface side is set at a position separated away by 100 μm fromthe outer surface 73, and a central portion 75 is set at a centerbetween the portion 72 on the inner surface side and the portion 74 onthe outer surface side.

[0052] Referring to FIG. 3 illustrating how to measure the X-raydiffraction image, the X-ray 76 is allowed to fall on the portion 72 onthe inner surface side (or portion 74 on the outer surface side) of thesample 70 at a Bragg angle θ with respect to the direction of thickness,and the X-ray 77 scattered at the Bragg angle θ is detected by a counter78. The dot diameter of the X-ray that is falling is 100 μm, and thedetails of the measuring conditions are as described in detail inExamples appearing later.

[0053]FIG. 4 is a diagram illustrating how to find a peak position A°(or B°) and a half-value width C° (or D°) from the image of diffractedintensity distribution of X-ray diffuse scattering. That is, when a lineis drawn in parallel with the abscissa passing through points ofone-half the intensity at the peak position A°, the half-value width C°is a distance between the two points at where the parallel lineintersects the peak.

[0054]FIG. 5 illustrates a relationship between the peak positions inthe X-ray diffuse scattering and the half-value widths of the peaksconcerning the centers in the bottom portions of various polyesterbottles.

[0055]FIG. 6 illustrates a relationship between the difference (B−A) inthe peak positions measured as described above and the difference (C−D)in the half-value widths concerning the polyester bottles.

[0056] The following facts will be obvious from the above results. Inthe following description, the subject portion is limited to the centerin the bottom portion of the bottle and, hence, the positions are simplyspecified as a portion on the outer surface side and a portion on theinner surface side.

[0057] I. In some bottles formed from preforms obtained by the injectionmolding, a peak position A at a portion on the outer surface side mayexceed 20.50°. In the bottle of the present invention, the peak positionB at the portion on the inner surface side as well as the peak positionA on the outer surface side are included in a range of from 19.45 to20.50°.

[0058] II. In the bottle of the present invention, the peak position Aat the portion on the outer surface side has an angle lower than that ofthe peak position B at the portion on the inner surface side at thecenter of the bottom portion, and the difference (B−A) therebetween isnot smaller than 0.15 degrees. However, these requirements are satisfiedby neither many bottles obtained from the known injection-moldedpreforms nor by the bottles from the compression-molded preforms havingdeviated thicknesses.

[0059] III. In the bottle of the present invention, further, thehalf-value width (C) of the X-ray diffuse scattering peak is larger thanthe half-value width (D) of the X-ray diffuse scattering peak at theportion on the inner surface side, and the difference (C−D) therebetweenis not smaller than 0.10 degrees in addition to the above-mentionedrequirement. However, the above-mentioned requirements II and III arenot simultaneously satisfied by the bottles lying outside the scope ofthe present invention.

[0060] In general, the strain due to orientation by fluidization islarge in the portion on the outer surface side where there is nohindrance in the fluidizing direction and is small in the portion on theinner surface side where there is a hindrance in the fluidizingdirection. At the center in the bottom portion of the bottle having suchstrain due to orientation by fluidization, it is believed that the X-raydiffuse scattering peak appears on the side close to 2θ=21° in theportion on the outer surface side, and appears on the side of a lowangle in the portion on the inner surface side. It is further believedthat the half-value width of the X-ray diffuse scattering peak is narrowin the portion on the outer surface side compared to the one in theportion on the inner surface side.

[0061] In the bottle of the present invention, on the other hand, thepeak position (A) in the portion on the outer surface side has an anglelower than that at the peak position (B) in the portion on the innersurface side, the difference (B−A) thereof is not smaller than 0.15degrees, the half-value width (C) of peak in the portion on the outersurface side is larger than the half-value width (D) of peak in theportion on the inner surface side, and the difference (C−D) thereof isnot smaller than 0.10 degrees, manifesting that the strain due toorientation by fluidization does not substantially exist at the centerin the bottom portion.

[0062] The bottle according to the present invention has little straindue to orientation by fluidization in the bottom portion, the bottomportion being uniformly and homogeneously stretched, having improvedshock resistance and buckling strength, having excellent resistanceagainst environmental cracking at the center of the bottom portion,without developing crazing or whitening during the preservation, andexhibiting excellent appearance.

[0063] [Resin]

[0064] In the present invention, any plastic material can be usedprovided it is capable of being stretch-blow-molded and thermallycrystallized, such as thermoplastic polyester and, particularly,ethylene terephthalate thermoplastic polyester. It is, of course,allowable to use other polyesters such as polybutylene terephthalate,polyethylene naphthalate, or a blend thereof with a polycarbonate or anallylate resin; acryl-butadiene-stylene copolymer (ABS resin);polyacetal resin; nylons such as nylon 6, nylon 66, a copolymerizednylon thereof; acrylic resins such as poly(methyl methacrylate);polypropylene; polystylene; as well as low-, middle- or high-densitypolyethylene, ethylene/propylene copolymer, ethylene/butene-1 copolymer,stylene/butadiene thermoplastic elastomer, cyclic olefin copolymer. Tothese plastics, various additives such as coloring agent, ultra-violetray absorbing agent, releasing agent, lubricant and nucleating agent canbe added, provided that the quality of the product is not affected.

[0065] In the ethylene terephthalate thermoplastic polyester used in thepresent invention, most of the ester recurring units and, generally, notless than 70 mol % and, particularly, not less than 80 mol % thereof areoccupied by an ethylene terephthalate unit. It is desired to use athermoplastic polyester having a glass transition point (Tg) of from 50to 90° C. and, particularly, from 55 to 80° C. and having a meltingpoint (Tm) of from 200 to 275° C. and, particularly, from 220 to 270° C.

[0066] It is desired to use a homopolyethylene terephthalate from thestandpoint of resistance against the heat and pressure. It is, however,also allowable to use a copolymerized polyester containing small amountsof an ester unit other than the ethylene terephthalate unit.

[0067] As the dibasic acid other than the terephthalic acid, there canbe exemplified aromatic dicarboxylic acids such as isophthalic acid,phthalic acid, and naphthalenedicarboxylic acid; alicyclic dicarboxylicacids such as cyclohexanedicarboxylic acid and the like acid; andaliphatic dicarboxylic acids such as succinic acid, adipic acid, sebacicacid and dodecanedionic acid, which may be used in one kind or in acombination of two or more kinds. As the diol component other than theethylene glycol, there can be used propylene glycol, 1,4-butane diol,diethylene glycol, 1,6-hexylene glycol, cyclohexane dimethanol orethylene oxide adduct of bisphenol A, which may be used in one kind orin two or more kinds.

[0068] It is also allowable to use a composite material obtained byblending the ethylene terephthalate thermoplastic polyester with apolyethylene naphthalate, a polycarbonate or a polyarylate having arelatively high glass transition point in an amount of from about 5% toabout 25% in order to enhance the strength of the material underrelatively high temperature conditions.

[0069] It is further allowable to use the polyethylene terephthalate andthe above-mentioned material having a relatively high glass transitionpoint which are laminated one upon the other.

[0070] The ethylene terephthalate thermoplastic polyester should atleast have a molecular weight large enough for forming a film. Dependingupon the applications, there is used the one of the injection grade orof the extrusion grade. It is desired that its inherent viscosity (I.V.)is generally from 0.6 to 1.4 dL/g and, particularly, from 0.63 to 1.3dL/g.

[0071] [Preform and its production]

[0072] In the present invention, it is desired to use a preform obtainedby subjecting the thermoplastic resin to the compression molding and,particularly, to the one-stage compression molding.

[0073] It was mentioned already that the strain due to orientation byfluidization does not substantially exist in the bottom portion of thepreform obtained by the compression molding method, and there isobtained a bottle having excellent properties. In addition to this,however, there can be obtained many advantages as will be describedbelow.

[0074] In the compression molding, unlike the injection molding, theprocessing can be effected at a relatively low temperature and,particularly, a pre-molded article for blow-molding is obtained by theheat-melting and the compression molding of one time, causing the resinto be less thermally deteriorated and making it possible to obtain ablown bottle having excellent properties.

[0075] That is, a cheap resin can be used for producing the blow-moldedarticle having the same properties (strength, shock resistance) and whenthe same starting resin is used, there can be obtained the blow-moldedbottle having superior properties. The bottle can be easily moldedthrough the preform even when use is made of a starting resin having ahigh viscosity which is not suited for being injection-molded. Inparticular, it is allowed to obtain a large blow bottle that requires alarge shock resistance.

[0076] In the one-stage compression molding method, it is desired thatthe amount of heat possessed by the mass of the molten resin iseffectively utilized at the time of melt-extruding the resin, that themass is prevented from being locally cooled as much as possible and,particularly, a portion of the mass of melt forming the bottom portionof the preform is not cooled, and that the movement of the resin on thesurfaces of the metal mold is not limited during the compressionmolding, from the standpoint of producing a preform having homogeneousinternal texture and excellent draw-blow moldability.

[0077] That is, in order that the orientation characteristics due toX-rays at the center in the bottom portion of the final bottle satisfythe above-mentioned requirements, the difference between the maximumthickness and the minimum thickness (tmax−tmin) of the barrel portion ofthe preform in the circumferential direction may be set to be not largerthan 0.07 mm by taking the above-mentioned conditions intoconsideration.

[0078] For this purpose, the mass of melt of nearly a predeterminedamount formed by cutting the extruded product is supplied into thefemale mold (cavity mold) without substantially permitting thetemperature to drop, and the mass of melt that is supplied is readilycompression-molded by using the metal mold (core mold).

[0079] Further, the preform having a bottom portion, a barrel portionand a mouth portion is compression-molded while quickly discharging theair remaining in the metal mold.

[0080] In the one-stage compression molding method, a drop in thetemperature of the resin from when it is cut into a mass of melt untilwhen it is thrown into the metal mold, seriously affects the homogeneityof the texture in the barrel portion with bottom of the preform that isto be stretch-blow-molded, draw orientation property and properties ofthe finally blow-molded articles and, particularly, shock resistance.The effect of a drop in the temperature appears conspicuously in thelower portion of the molten mass that forms the bottom portion of thepreform (bottom portion of the finally blow-molded article).

[0081] That is, when the lower portion of the molten resin mass islocally cooled, the degree of strain increases in the bottom portion ofthe preform causing the finally blow-molded article to exhibit poorappearance and a decreased shock resistance.

[0082] In the one-stage compression molding method, a drop in thetemperature of the mass of molten resin is substantially suppressed fromwhen the molten resin is cut into a mass of melt until when it is throwninto the metal mold and, particularly, a drop in the temperature of thelower portion of the mass of molten resin is suppressed within theabove-mentioned period of time, in order to effectively solve theabove-mentioned troubles.

[0083] In order to suppress the drop in the temperature of the mass ofmelt as described above, the mass of melt should be avoided fromcontacting to other members except the holding portion after the melt iscut into the mass of melt until when it is thrown into the metal mold.In particular, contact should be avoided as much as possible between thelower portion of the mass of melt and other members.

[0084] For this purpose according to a preferred method of production,the molten polyester is cut in parallel with the axial direction of themale mold (core) and the female mold (cavity), and the mass of melt thatis cut is supplied into the metal mold substantially maintaining ahorizontal state.

[0085] In order to supply the mass of melt in nearly a predeterminedamount and to avoid the lower portion thereof from being cooled as muchas possible, further, it is desired that the mass of molten resin is fedin shape form of a cylinder or in a shape close to the cylinder.

[0086] Moreover, in order to avoid the drop in the temperature in thelower portion of the mass of melt as much as possible and to stablysupply the mass of melt, i.e., to prevent the mass of melt from falling,it is desired that the mass of melt is held at a position higher thanthe center of gravity thereof, and is moved from the cut position to theposition of the metal mold and is supplied into the metal mold.

[0087] In order to avoid the mass of melt from being cooled, it isdesired that the mass of melt is thrown into the metal mold within aperiod of time as short as possible after it is cut into the mass andthat the molding is started within a period of time as short as possibleafter it is thrown into the metal mold. Generally, it is recommendedthat the mass of melt is thrown into the metal mold within one secondafter it is cut, and is molded within 0.5 seconds after it is throwninto the metal mold.

[0088] In the one-stage compression molding, it is quite important thatthe compression molding is effected while expelling the air remaining inthe bottom of the metal mold or remaining in the vicinities thereof.That is, under the condition where the air remains in the metal mold,wrinkles tend to develop in the portions adhered to the metal mold or inthe vicinities thereof. When the air is quickly expelled after the startof the molding, on the other hand, development of wrinkles iseffectively prevented. Occurrence of the wrinkles is attributed to thatthe portions intimately adhered to the surface of the metal mold and theportions not intimately adhered to the surface of the metal mold arearranged maintaining fine gaps, which is believed to be a phenomenonspecific to the compression molding. Under the conditions where the airis expelled, it is considered that the resin is intimately adhered againto the surface of the metal mold to form the container wall withoutwrinkles.

[0089] To expel the air remaining on the surface of the female metalmold, escape passages for the residual air may be formed from themolding portion to the external side, and no particular limitation isimposed on this means. For instance, the female metal mold may beprovided with fine gaps or a porous portion in the bottom portionthereof or in the vicinities thereof. Further, it is particularlyeffective if the residual air is forcibly expelled by using an externalvacuum pump simultaneously with the start of the molding.

[0090] In the one-stage compression molding method, the female metalmold and the male metal mold may have such shapes and structures as tomold the barrel portion with bottom and the mouth portion. Though thereis no particular limitation, it is generally desired that the male metalmold comprises a core metal mold and a follower metal mold thatsurrounds the core metal mold and is allowed to be opened and closed inconcentric therewith, that the tapered portion with bottom is molded bythe core metal mold and the female metal mold (cavity mold), and thatthe mouth portion is molded by the core metal mold and the followermetal mold.

[0091] In this case, the follower metal mold is reciprocally movedtogether with the core metal mold. The follower metal mold is alwaysurged toward the female metal mold due to the urging means such asspring. At the bottom dead center of the core metal mold, the core metalmold and the follower metal mold are maintained in a state of beingcontacted to each other at all times.

[0092] Despite there is a small change in the amount of the mass ofmolten resin, therefore, there is always formed a preform having themouth portion of a predetermined shape maintaining a predeterminedheight (from the inner surface of the bottom portion to the top surfaceof the mouth portion) at all times, the mouth portion being importantfor accomplishing the sealing. A change in the amount of the mass ofmolten resin can be absorbed relying on the mesh of the core metal moldand the female metal mold (cavity metal mold), i.e., relying on thethickness of the barrel portion with bottom of the preform that isformed.

[0093] In general, the outer periphery of the mouth portion of thebottle is provided with a support ring for supporting the bottle at thetime of filling the bottle with the content, and the structure of themouth portion is formed in the stage of forming the preform. Accordingto the present invention, however, an annular groove is formed in theinner peripheral edge portion in the lower surface of the support ring.Owing to this annular groove, a change in the mass of molten resin isabsorbed as a change in the height of the annular groove, whereby thethickness of the preform is prevented from changing and the wall of thepreform acquires a homogeneous texture. The annular groove also remainsin the bottle formed from the preform and works to suppress a change inthe thickness of the bottle as a matter of course.

[0094] The mass of the molten resin can be supplied nearlyquantitatively by melt-extruding the resin through an extruder and,further, through a gear pump and cutting the resin at a predeterminedtiming. Still, however, the amount of supplying the resin inevitablyvaries within a certain range. According to the above-mentioned moldingsystem, this variation can be easily absorbed.

[0095] In the one-stage compression-molding method, some degree ofpressure may be necessary for preventing the loss at the time of moldingbut the molding force may generally be considerably small offering anadvantage. Compared to the injection-molding apparatus, therefore, thecompression-molding apparatus is constructed in a considerably smallsize to decrease the cost of the apparatus.

[0096] The preform for blow-molding used in the present invention isformed by compression molding a molten resin such as polyester orpolypropylene, and has the mouth portion of a shape and a sizecorresponding to the mouth portion of the finally molded article, andhas a barrel portion with bottom that is to be blow-molded, as well as afeature in that the strain due to orientation by fluidization does notsubstantially exist in the closed bottom portion and no gate portion isincluded, either.

[0097] The gate portion present in the preform with bottom obtained bythe injection molding causes a great deal of problem with respect toproductivity, cost of production and properties of the finallyblow-molded article. However, the preform used in the present inventionhas no gate portion and, hence, requires no step of cutting and does notproduce scrap resin. Besides, the central portion on the bottom issmooth causing neither crystallization or whitening.

[0098] In the preform for blow-molding used in the present invention,further, no wrinkle develops in the bottom portion or in the vicinitiesthereof since the molding is carried out under the above-mentionedstrict temperature control and under the conditions of expelling theresidual air.

[0099] The above-mentioned preform for blow-molding has no strain due toorientation by fluidization, no gate and no wrinkle in the bottomportion, and features very excellent smoothness and homogeneity in thetexture. Therefore, the blow-molded article obtained bystretch-blow-molding the preform has very excellent appearance and shockresistance in the bottom portion.

[0100] Further, the preform makes it possible to produce a blow-moldedarticle which permits the resin to be thermally deteriorated little asdescribed earlier and features excellent properties such as tensilestrength, resistance against the pressure, shock resistance and heatresistance.

[0101] [Compression-Molding Apparatus]

[0102] Referring to FIG. 7 (plane view) and FIG. 8 (side view)illustrating the whole arrangement of the apparatus used in theone-stage compression-molding method, the apparatus roughly comprises aresin extruder device 10, a device 20 for cutting and feeding a mass ofmelt, and a compression-molding device 30 for forming a preform.

[0103] The extruder device 10 is provided with an extruder main body 11for melting and kneading the resin. A vacuum hopper 12 is provided onthe inlet side of the main body to hold, in dry state, the powder orpellets of the thermoplastic resin that is to be molded and to feed itto the extruder main body. On the outlet side of the main body, thereare provided a suction vent 13 for sucking and removing decomposed gasesin the resin, and a die head 14 for receiving the extruded molten resin.

[0104] The die head 14 is connected to an extruder nozzle 16 through aconduit 15. Here, it is desired to provide a gear pump 17 between thedie head 14 and the extruder nozzle 16 to supply the molten resin in apredetermined amount. FIG. 8 does not show the gear pump 17 to avoid thedrawing from becoming complex.

[0105] Referring to FIGS. 9 and 10, the device 20 for cutting andfeeding the mass of melt comprises a cutter 22 provided on a rotaryturret 21, and a combination of an outer grip member 23 for gripping themass of melt and an inner grip member 24. The cutter is tilted withrespect to the radial direction of the turret 21 and cuts the melt 18 ofthe resin extruded from an extruder nozzle 16 in a direction at rightangles with the direction of extrusion.

[0106] The outer grip member 23 comprises a portion extending in theradial direction of the turret and an outer portion extending in thecircumferential direction, and is secured to the turret 21. On the otherhand, the inner grip member 24 is allowed to move in the radialdirection of the turret relative to the outer grip member 23.

[0107] The rotary turret 21 of the cutting/feeding device 20 is soprovided as to pass under the extruder nozzle 16 of the extruder device10 and over a female metal mold 32 of the lower compression-moldingdevice 30. Under the extruder nozzle 16, the melt 18 is gripped by thegrip members 23 and 24, and is cut by the cutter 22. The mass 19 of meltis moved over the female metal mold being gripped by the grip members 23and 24, and the mass 19 of melt is released from the grip members 23 and24, and is thrown into the female metal mold 32.

[0108] From FIGS. 7 to 10, it will be obvious that in the one-stagecompression-molding apparatus, the melt 18 of the thermoplastic resin isextruded in parallel with the axial direction of the male metal mold 33and the female metal mold 32, and the mass 19 of melt that is cut is fedinto the female metal mold 32 in a state of being maintainedsubstantially in parallel, that the mass 19 of melt is supplied innearly a predetermined amount due to the gear pump 17 and in acylindrical shape or in a shape close to the cylinder, and that the mass19 of melt is gripped at a portion higher than the center of gravitythereof by the grip members 23 and 24, and is moved from the cuttingposition C to the position M of the metal mold so as to be fed into themetal mold 32.

[0109] Roughly speaking, the compression-molding apparatus 30 comprisesa rotary turret 31, and combinations of many female metal molds (cavitymetal molds) 32 and male metal molds (core metal molds) 33 arrangedsurrounding the rotary turret.

[0110] The rotary turret 31 is provided with the above-mentionedmechanism 20 for cutting and feeding the mass of melt, and a mechanism34 for taking out the preform for blow-molding that is molded.

[0111] The rotary turret 31 is supported by a machine frame 35 through avertical shaft 36 in a horizontal direction so as to rotate, and isrotated by a motor 37 and a drive transmission mechanism 38.

[0112] Combinations (sets) of the female metal molds 32 and the malemetal molds 33 are secured in many number on the upper peripheralsurface of the rotary turret 31. That is, the female metal mold 32 issecured on the rack 39, whereas the male metal mold 33 is provided so asto move up and down in concentric with the female metal mold 32 owing toa lift drive mechanism 42 such as hydraulic mechanism through a verticalsupport member 40 and a horizontal support member 41.

[0113] In FIGS. 11 and 12 which illustrates the structures of the femalemetal mold 32 and the male metal mold 33 in detail and the steps ofmolding, the female metal mold 32 has a cavity 43, vent portions 44 inthe bottom portion thereof for expelling the residual air, and ventportions 45 in a portion connecting the bottom portion to the taperedportion.

[0114] Upwardly directed small protuberances 46 are formed surroundingthe upper portion of the cavity 43. The operation will be describedlater.

[0115] Further, a slidable ring-like follower member 47 is providedaround the female metal mold 32 in concentric therewith. The followermember 47 has a shaft 48 extending downward, and has a stopper 49 formedat the lower end thereof, the stopper 49 being fitted in a recess 50 inthe lower portion of the female metal mold 32. It will thus be obviousthat the stopper 49 is allowed to move up and down between the uppersurface and the lower surface of the recess 50. The stopper 49 is urgedupward by a means such as a spring (not shown) or the like. Further, atapered portion 51 for engagement having a diameter increasing upward,is formed in the inner peripheral surface in the upper part of thefollower member 47.

[0116] The male metal mold 33 is equipped with a core metal mold 53secured to a support member 52 that can be moved up and down. The coremetal mold 53 includes a portion 54 for forming the top surface of themouth portion of the preform, a portion 55 for forming the innerperipheral surface of the mouth portion, and a portion 56 for formingthe inner surface of the tapered barrel portion with bottom.

[0117] The core metal mold 33 is surrounded by the follower metal mold57 that is allowed to be opened and closed in concentric therewith. Thefollower metal mold 57 is secured to a follower support member 58.Though not diagramed, a push spring is provided between the supportmember 52 and the follower support member 58 to urge the follower metalmold downward.

[0118] On the lower inner peripheral surface of the follower metal mold57 is formed a portion 59 for forming the inner peripheral surface ofthe mouth portion of the preform. On the other hand, on the lower outerperipheral surface thereof is formed a tapered portion 60 for engagementhaving a diameter decreasing downward.

[0119] In the compression-molding apparatus shown in FIGS. 11 and 12,the pushing forces (absolute values) of the members are set as describedbelow to smoothly conduct the operations.

[0120] Pushing force of the male mold 33>pushing force of the followermember 47>pushing force of the follower metal mold 57

[0121] The above-mentioned apparatus performs the molding operation asdescribed below.

[0122] (A) Step of extruding the melt:

[0123] The thermoplastic resin is fed into the vacuum hopper 12 of theextruder 10, melted and kneaded by the barrel and screw in the extrudermain body 11 in vacuum state without moisture of the external air, fedto the nozzle 16 through the die head 14 and the conduit 15 in apredetermined amount due to the gear pump 17, and is extruded into acylindrical shape through the nozzle 16.

[0124] (B) Step of cutting and feeding:

[0125] The resin flow 18 melt-extruded from the nozzle 16 is cut by acutter 22 into a mass 19 of melt of a cylindrical shape or of a shapeclose to the cylinder. The mass 19 of melt is gripped by the gripmembers 23 and 24, is moved from the cutting position C to the positionM for feeding into the female metal mold 32 accompanying the turn of theturret without substantially permitting the temperature to drop, and isthrown into the female metal mold 32.

[0126] (C) Step of compression molding:

[0127] In a step of approach designated at I in FIG. 11, the cavitymetal mold 43 and the core metal mold 53 are still opening, and the mass19 of melt is accommodated in an erected state in the cavity 43. Thecore metal mold 53 starts descending.

[0128] In a step of fastening the cavity metal mold designated at II inFIG. 11, the core metal mold 53 descends into the cavity, and spacedefined by the cavity 43 and the core 53 is nearly filled with themolten resin 19′. Simultaneously with the start of the compressionmolding, the air remaining in the cavity is quickly expelled to theexternal side through the vent portions 44 and 45.

[0129] At the same time, the follower metal mold 57 descends to come incontact with the follower member 47, but there still exists a gapbetween the upper surface of the follower support member 58 and thelower surface of the male metal mold support member 52.

[0130] In a step of fastening the core metal mold designated at III inFIG. 11, the core metal mold 53 further descends, and the upper surfaceof the follower support member 58 comes in contact with the lowersurface of the male metal mold support member 52. Therefore, the moltenresin 19′ in the cavity flows into space defined by the core metal mold53 and the follower metal mold 57.

[0131] In a step of solidification at a high temperature designated atIV in FIG. 11, the core metal mold 53 further descends to some extent,and the follower member 47 descends accompanying thereto, so that spacedefined by the cavity 43, core metal mold 53 and follower metal mold 57is filled with the resin.

[0132] In a step of solidification at a low temperature designated at Vin FIG. 11, the volume of the resin contracts, i.e., whiskers developdue to a drop in the resin temperature. However, the strain caused bythe contraction of volume can be absorbed by applying a compressiveforce to the male metal mold (core 53).

[0133] In this case, it becomes necessary, as a matter of course, to somove the core metal mold 53 and the cavity metal mold 43 as to come inmesh together. Upon bringing the upwardly directed small protuberances46 of the cavity metal mold 43 into mesh with the follower metal mold57, however, it becomes possible to absorb the contraction of the volumeand to obtain a preform for blow-molding without strain. A portion atwhich the upwardly directed small protuberances 46 are brought in meshwith the follower metal mold 57, forms the above-mentioned annulargroove in the preform.

[0134] The steps for taking out the compression-molded preform aredesignated at I to IV in FIG. 12. In a step I, the molding is finished.In a step II, the core metal mold 53 starts rising; i.e., the metal moldstarts opening. In a step III, the core metal mold 53 rises earlier thanthe follower metal mold 57 to remove the core from the preform 60 thatis molded. In a step IV, the core metal mold 53 further rises and thepreform 60 is taken out of the cavity 43. In a step V, at a positionwhere the core metal mold rises again, the follower metal mold 57 movesto a position (indicated by a dotted line) on the outer side of itsdiameter to release the preform 60 for blow-molding that is held.

[0135] [Molding Conditions]

[0136] When the thermiplastic polyester is used, the temperature (diehead temperature) for melt-extruding the thermoplastic polyester resinlies, preferably, in a range of Tm+100° C. to Tm+10° C. and,particularly, Tm+40° C. to Tm+20° C. with the melting point (Tm) of thethermoplastic polyester resin as a reference, though the thermoplasticresin used in the present invention may vary depending upon the kind ofthe resin.

[0137] When the temperature is lower than the above-mentioned range, theshearing speed becomes too great that it often becomes difficult to forma uniformly melt-extruded product. When the temperature is higher thanthe above-mentioned range, on the other hand, the resin is thermallydeteriorated to a great extent or the draw-down becomes conspicuous.

[0138] The weight of the mass of the melt to be cut is determined by thefinally blown bottle as a matter of course, but is, generally, selectedfrom a range of 100 to 2 g and, particularly, 40 to 10 g to meet therequired strength.

[0139] The mass of melt can be easily handled when it has a cylindricalshape or a shape close thereto. The mass of melt has a ratio (H/D) ofthe height (H) to the diameter (D) of, generally, from 0.8 to 4 from thestandpoint of preventing a drop in the temperature of the mass of meltas much as possible and easily throwing the mass of melt into the femalemetal mold.

[0140] That is, when the ratio H/D lies outside the above-mentionedrange, the surface area of the mass of melt increases and thetemperature tends to drop.

[0141] Any cutter can be used for cutting the mass of molten resin and,preferably, the one capable of preventing the sticking of resin. Thesurface treatment such as shot-blasting the surfaces of the tool isparticularly effective.

[0142] As the grip members for moving the mass of molten resin, thereare used those made of a material having good heat-insulating propertyand having areas contacting to the resin as small as possible.

[0143] It is desired that the mass of the molten resin is thrown intothe metal mold quickly and within a period of time described alreadyafter it is cut.

[0144] As the compression-molding metal mold, there is used the onehaving fine gaps or a porous portion in the bottom portion or in thevicinities thereof, the fine gaps being formed by dividing the bottomportion or the vicinities thereof into several pieces or by formingholes in the metal mold for expelling the air. The porous portion isformed by machining, for example, a sintered metal or the like.

[0145] The surface temperature of the compression-molding metal mold maybe the one at which the molten resin is solidified and will, preferably,be from 65 to 30° C. in the case of a polyester. In order to maintainthe surface temperature of the metal mold to lie within theabove-mentioned range, it is desired that a medium such as cooling wateror temperature-controlled water is passed through the metal mold.

[0146] One of the features is that a considerably small molding force isrequired for the compression molding. The molding force may differ to aconsiderable degree depending on the kind of the resin and the size ofthe preform for blow-molding. Generally, however, the molding force isfrom 800 to 50 kgf and, particularly, from 600 to 150 kgf.

[0147] Through the above-mentioned compression molding of one stage,there is obtained a preform for blow-molding without strain due tofluidized orientation in the bottom portion, without gate portion, andwithout requiring any trimming operation. Therefore, the preform can beused in its form in the step of draw-blow-molding offering manyadvantages such as simplifying the steps and enhancing the productivity.

[0148] [Preform for Blow-Molding]

[0149] Referring to FIG. 13 illustrating the preform for blow-molding ofthe present invention, the preform 60 roughly comprises a mouth portion61 and a tapered barrel portion 62 with bottom. The mouth portion 61becomes a mouth portion of the bottle which is a finally molded article.Around the outer periphery of the mouth portion 61 are formed anengaging portion 63 for the closure necessary for being sealed with theclosure and a support ring 64. The barrel portion 62 with bottom is aportion that is to be drawn and blow-molded and includes a tapered sidewall portion 65 and a bottom portion 66 smoothly continuous thereto andprotruding downward. As described already, the bottom portion 66 issubstantially free of strain caused by fluidized orientation, and hasneither residual gate portion nor wrinkles. The mouth portion 61 and thebarrel portion 62 with bottom are smoothly continuing through aconnection portion 67.

[0150] It will be obvious that an annular groove 68 is formed in theinner peripheral edge on the lower surface of the support ring 64.

[0151] The tapered side wall portion 65 and the bottom portion 66 havesizes and shapes that must lie within predetermined preferred rangesfrom the standpoint of compression moldability and moldability at thetime of draw-blowing that is finally effected. In general, it is desiredthat the side wall portion 65 has an outer surface of the shape of acircular truncated cone and the bottom portion 66 has an outer surfaceof the shape of a partial spherical surface smoothly continuing to thesurface of the circular truncated cone, from the standpoint ofmoldability. However, they may have any shape to meet the shape of ablow-molded article.

[0152] The inner surface, too, of the side wall portion 65 is that ofthe circular truncated cone continuous through the inclined portion 67of which the thickness increases from the inner periphery of theconnection portion.

[0153] It is desired that the tapered angle (θ) on the outer surface ofthe side wall portion is from 0.5 to 89.5° from the standpoint ofmoldability.

[0154]FIG. 14 is a sectional view of the preform for blow-molding ofwhen the tapered angle is 0.8°, and FIG. 15 is a sectional view of thepreform for blow-molding of when the tapered angle is 45°.

[0155] The side wall portion 65 and the bottom portion 66 may haveuniform thicknesses except the inclined portion 67 or may havethicknesses that changes, e.g., the thickness of the side wall portionincreasing toward the bottom portion.

[0156] The above-mentioned preform may be directly subjected to thestretch-blow-molding, or the mouth portion may be crystallized andwhitened through the heat treatment in the stage of the preform in orderto impart heat resistance and rigidity to the mouth portion of thepreform. Or, after the preform is molded into a bottle by the biaxialstretch-blow-molding that will be described later, the mouth portion ofthe obtained plastic bottle may be crystallized and whitened.

[0157] [Stretch-blow-molding]

[0158] The preform is heated at a drawing temperature, and is pulled anddrawn in the axial direction and is blow-drawn in the circumferentialdirection to obtain a bottle.

[0159] The molding and the stretch-blow-molding of the preform can beaccomplished by the cold parison system as well as by the hot parisonsystem according to which the stretch-blow-molding is effected withoutcompletely cooling the preform formed by the compression molding.

[0160] Prior to effecting the stretch-blow-molding, as required, thepreform is pre-heated up to a temperature suited for the drawing by suchmeans as the hot air, infrared-ray heater or high-frequency inductionheating. In the case of the polyester, the temperature range is from 85to 120° C. and, particularly, from 95 to 110° C.

[0161] The preform is fed into a stretch-blow-molding machine that hasbeen known per se., set into the metal mold, pulled and drawn in theaxial direction by inserting a drawing rod, and is blow-molded in thecircumferential direction by blowing a fluid.

[0162] It is desired that the final bottle has a drawing ratio of from1.5 to 25 times in terms of an area ratio, and that the drawing ratio inthe axial direction is from 1.2 to 6 times and the drawing ratio in thecircumferential direction is from 1.2 to 4.5 times.

[0163] The stretch-blow-molded bottle can be thermally set by a knownmeans. The thermal setting can be effected in a blow-molding metal moldrelying on a one-mold method or in a thermosetting metal mold separatefrom the blow-molding metal mold relying on a two-mold method. Thethermosetting is effected preferably at a temperature of from 100 to200° C.

EXAMPLES

[0164] The invention will be further described by way of followingExamples.

[0165] [Preparation of Containers]

[0166] The containers were prepared in a manner as described below andwere used for the following experiment.

[0167] (1) Compression-molding of the preforms.

[0168] A polyethylene terephthalate resin EFS-7H manufactured by KaneboGosen Co. was dried in a drier, vertically extruded through a nozzlehaving a diameter of 22 mm by using an extruder of a diameter of 65 mmand L/D of 27, and the resin in a molten state was horizontally cut byusing a cutter rotating in a horizontal direction to obtain a mass ofmelt of a weight of 20 g, immediately conveyed, permitted to verticallyfall into a female metal mold in the molding machine rotating insynchronism with the rotation of the cutter, compression-molded whileclosing the metal mold at a high speed and expelling the residual air inthe metal mold, solidified by cooling for about 12 seconds whileapplying a force of about 700 kgf, and the metal mold was opened toobtain a preform for blow-molding having a mouth of a diameter of 38 mm,a height of 63 mm, an average thickness of 3 mm and a weight of 20 g.

[0169] (2) Injection-molding of the preforms.

[0170] The preforms were molded in the same manner as described abovebut effecting the molding using an injection-molding machine (FE-160,manufactured by Nissei Jushi Kogyo Co.) under the following conditions:

[0171] Temperature setting: C1/C2/C3/RSnozzle/nozzle/HR=275/285/285/285/290/290

[0172] Cycle time: 25.9 seconds

[0173] (3) Stretch-blow-molding of the bottles.

[0174] The preform was heated in a draw-blow machine at 110° C., drawnin the vertical direction in the blow metal mold and was, then,blow-molded with a high-pressure air of 35 atms. to obtain a bottlehaving a height of 140 mm, a barrel diameter of 67.5 mm and a content of380 ml.

[0175] [Testing method]

[0176] {circle over (1)} Preservation test.

[0177] Ten empty bottles obtained by biaxially stretch-blowing athermoplastic polyester were preserved under the conditions of 30° C.and 90% RH for three weeks. After preserved, the central portions in thebottom of the bottles were observed by eyes with respect to theoccurrence of crazing and whitening. The results were expressed as thefrequency of occurrence of the crazing and the whitening.

[0178] {circle over (2)} Measurement of axial load.

[0179] A bottle obtained by biaxially stretch-blowing the thermoplasticpolyester was filled with 350 ml of water and was sealed with a cap. Theaxial load strength of the bottle in the vertical direction was measuredby using the TENSILON (UCT-5T)(manufactured by Orientek Co.) at acrosshead speed of 50.0 mm/min. to find the yield strength.

[0180] {circle over (3)} X-ray measurement.

[0181] A central portion in the bottom of the bottle obtained bybiaxially stretch-blowing the thermoplastic polyester was cut into athickness of 1 mm and was measured for its diffraction peak by using avery small X-ray diffraction (PSPC-150C)(manufactured by Rigaku DenkiCo.). The direction of the sample was such that the direction ofthickness of the bottom portion was in the direction of height of themeasuring surface.

[0182] The measurement was taken under the conditions of a tube voltageof 30 KV, a tube current of 100 mA, a collimator of 100 μm and ameasuring time of 1000 seconds, and at three points, i.e., pointsseparated away by 100 μm from the inner surface and from the outersurface, and at an intermediate point from the inner surface and fromthe outer surface. After the measurement, the integrated intensitieswere calculated over a range of from 10.071 degrees to 30.071 degrees,to find a peak position and a half-value width.

[Example 1]

[0183] Preforms having a weight of 20 g were molded by compressionmolding. The preforms possessed a uniform thickness in the barrelportion in the circumferential direction (max. thickness−min.thickness=0.07 mm or smaller), and were biaxially stretch-blow-molded toobtain bottles. The difference in the thickness (max. thickness−min.thickness) of the barrel port-on of the bottles in the circumferentialdirection was about 0.06 mm or smaller. Preservation testing of thebottles proved that no crazing or whitening occurred on ten bottles, andthe appearance was the same as before the preservation testing.Measurement of the axial load proved the yield strength to be 46.0 kgfsatisfying properties required by the bottles for beverages.

[Example 2]

[0184] Preforms having a weight of 20 g were molded by the compressionmolding and the injection molding.

[0185] The preforms obtained by the compression molding included thosehaving uniform thickness in the barrel portion in the circumferentialdirection (max. thickness−min. thickness=0.07 mm or smaller) and thosehaving nonuniform thicknesses (max. thickness−min thickness=0.08 to 0.15mm). The preforms obtained by the injection-molding all possesseduniform thickness in the barrel portion in the circumferentialdirection. These preforms were biaxially drawn and blow-molded to obtainbottles.

[0186] The bottles obtained from the preforms produced by thecompression molding and having nonuniform thicknesses in the barrelportion in the circumferential direction, exhibited a difference in thethickness (max. thickness−min. thickness) in the barrel portion in thecircumferential direction of from 0.15 to 0.06 mm, whereas the bottlesobtained from other preforms exhibited a difference in the thickness ofthe barrel portion in the circumferential direction of not larger thanabout 0.06 mm.

[0187] These bottles were measured by using X-rays. The results were asshown in Table 1 below. TABLE 1 Thickness of bottle DifferenceDifference Preform in circum- Peak in position Half-value in half-valuemolding ferential position (°) (°) width (°) width (°) method directionOut(A) In(B) B − A Out(C) In(D) C − D Compression uniform 19.647 20.0910.444 11.845 11.696 0.149 molding Compression nonuniform 20.186 20.164−0.022 11.673 11.492 0.181 molding Injection uniform 21.115 20.321−0.794 11.890 11.496 0.394 molding

[Comparative Example 1]

[0188] Preforms having a weight of 20 g were molded by the injectionmolding. The obtained preforms were biaxially drawn and blow-molded toobtain bottles. After the preservation testing of the bottles, crazingof about 2 mm occurred in the central portion in the bottom of the fourbottles, and whitening of a diameter of about 10 mm occurred in theother three bottles.

[Comparative Example 2]

[0189] Preforms of a weight of 20 g were molded by thecompression-molding. The preforms possessed nonuniform thicknesses inthe barrel portions in the circumferential direction (max.thickness−min. thickness=0.08 to 0.15 mm). The preforms were biaxiallydrawn and blow-molded to obtain bottles. The obtained bottles exhibiteda difference in the thickness in the barrel portions in thecircumferential direction (max. thickness−min. thickness) of from 0.15to 0.06 mm. After the preservation testing of the bottles, crazing orwhitening occurred in none of the ten bottles, and the appearance wasthe same as before the preservation testing. In the measurement of axialload, however, the yield strength was 30.2 kgf failing to satisfy theproperties required by the bottles for beverages. The results of thepreservation testing and of the measurement of axial loads were as shownin Table 2 below. TABLE 2 Thickness of Preform bottle in moldingcircumferential Appearance Axial load method direction Crazing Whitening(kgf) Compression uniform 0 0 46.0 molding Compression nonuniform 0 030.2 molding Injection uniform 4 3 53.0 molding

[0190]

[0191] The present inventors have succeeded in detecting the strain dueto orientation by fluidization at the center in the bottom portion ofthe bottle, have molded the preform by subjecting the thermoplasticresin to the compression molding and, particularly, to the one-stagecompression molding, so that the strain due to orientation byfluidization will not substantially occur, and have subjected thepreform to the biaxial stretch-blow-molding, in order to produce abottle having a bottom portion that is homogeneously and uniformlystretched, having little strain due to orientation by fluidization inthe bottom portion and, as a result, exhibiting improved shockresistance and buckling strength in the bottom portion, featuringexcellent resistance against environmental cracking at the center in thebottom portion, without developing crazing or whitening during thepreservation, and offering excellent appearance.

What we claim is:
 1. A bottle formed by biaxially stretch-blow-molding athermoplastic resin and having a mouth portion, a shoulder portion, abarrel portion and a bottom portion, said bottom portion without beingsubstantially affected by the residual strain due to orientation byfluidization.
 2. A bottle according to claim 1, wherein said bottle isformed by biaxially stretch-blow-molding a preform that is formed bycompression-molding a thermoplastic resin.
 3. A bottle according toclaim 2, wherein a difference (tmax−tmin) between a maximum thicknessand a minimum thickness of the barrel portion of said preform in thecircumferential direction is not larger than 0.07 mm.
 4. A bottleaccording to claim 1, wherein the bottle is composed of a polyester andthe central portion in the bottom portion of the bottle has a diffusescattering peak in 28 of from 19.45 to 20.50° as measured by usingX-rays (Cu-α) falling in the direction of thickness of the containerwall, a peak position (A) at a portion on the outer surface side of thecentral portion in the bottom portion is an angle lower than that of apeak position (B) at a portion on the inner surface side of the centralportion in the bottom portion, the difference (B−A) thereof is notsmaller than 0.15 degrees, a half-value width (C) of the diffusescattering peak of X-rays in the portion on the outer surface side atthe central portion in the bottom portion is larger than a half-valuewidth (D) of the diffuse scattering peak of X-rays in the portion on theinner surface side at the central portion in the bottom portion, and thedifference (C−D) thereof is not smaller than 0.10 degrees.
 5. A bottleaccording to claim 1, wherein the mouth portion has a support ring, andan annular groove is formed in the inner peripheral edge in the lowersurface of the support ring.
 6. A method of producing a bottle bybiaxially stretch-blow-molding a pre-molded article for blow moldingthat is obtained through the step of: extruding a molten thermoplasticresin and cutting it into a mass of melt of nearly a predeterminedamount; arranging a male metal mold and a female metal mold so as tomove relative to each other and feeding the mass of melt into the metalmold; compression-molding the mass of melt into a pre-molded articlehaving a barrel portion with bottom and an annular groove formed in theinner peripheral edge in the lower surface of the support ring; andcooling and solidifying the compression-molded article and dischargingthe molded article out of the metal mold.
 7. A method of producing abottle according to claim 6, wherein the mass of melt iscompression-molded into the pre-molded article while discharging the airremaining in the metal mold.
 8. A method of producing a bottle accordingto claim 6, wherein fine gaps or holes are formed in a portion of themetal mold forming the bottom portion of the pre-molded article.
 9. Amethod of producing a bottle according to claim 6, wherein the malemetal mold is constituted by a core metal mold and a follower metal moldsurrounding the core metal mold and is allowed to be opened and closedcoaxially therewith, the barrel portion with bottom is molded by thecore metal mold and the female metal mold, and the mouth portion ismolded by the core metal mold and the follower metal mold.